cmd/tsidp: use advertised env vars for config

Fixes #14491

Signed-off-by: Kot <kot@kot.pink>

cmd/tsidp/tsidp.go

@@ -65,9 +65,17 @@ var (
 	flagLocalPort          = flag.Int("local-port", -1, "allow requests from localhost")
 	flagUseLocalTailscaled = flag.Bool("use-local-tailscaled", false, "use local tailscaled instead of tsnet")
 	flagFunnel             = flag.Bool("funnel", false, "use Tailscale Funnel to make tsidp available on the public internet")
-	flagDir                = flag.String("dir", "", "tsnet state directory; a default one will be created if not provided")
+	flagHostname           = flag.String("hostname", envOr("TS_HOSTNAME", "idp"), "tsnet hostname to use instead of idp")
+	flagDir                = flag.String("dir", envOr("TS_STATE_DIR", ""), "tsnet state directory; a default one will be created if not provided")
 )
 
+func envOr(key, defaultVal string) string {
+	if result, ok := os.LookupEnv(key); ok {
+		return result
+	}
+	return defaultVal
+}
+
 func main() {
 	flag.Parse()
 	ctx := context.Background()
@@ -121,7 +129,7 @@ func main() {
 		defer cleanup()
 	} else {
 		ts := &tsnet.Server{
-			Hostname: "idp",
+			Hostname: *flagHostname,
 			Dir:      *flagDir,
 		}
 		if *flagVerbose {